Millions of women used Prempro and other HRT drugs up until 2002, when the groundbreaking Women’s Health Initiative study found that taking the drugs significantly increased women’s risk of breast cancer and death from cardiovascular disease. The risk was so striking that researchers called an early halt to the study out of concern for participants’ lives. The drugs were — and still are — marketed to relieve the symptoms of menopause, such as hot flashes, mood swings and night sweats.

More recent research suggests that HRT drugs also increase women’s risk of dying from lung cancer.

Although Prempro was marketed by Wyeth, Pfizer assumed liability for Wyeth’s prior actions when it purchased the company in October.

According to Barton’s lawyers, Wyeth was aware of the risks of Prempro well before the release of the Women’s Health Initiative results, but made no efforts to withdraw the drug from the market or warn women or doctors of its effects.

“They knew back in the 1970s that these drugs had the potential to cause breast cancer,” said attorney Esther Berezofsky, “so they didn’t have the studies done.” When negative results began to emerge, Berezofsky said, Wyeth attempted to downplay them.

The jury agreed, ruling not only that Prempro had caused Barton’s case of invasive breast cancer, but that the drug company was to blame.

Before its acquisition, Wyeth also admitted to practices such as ghostwriting articles for publication in medical journals, promoting off-label (unapproved) uses of drugs and making lavish gifts to doctors. Pfizer claims the company has since abandoned these policies.

The Barton case is only one of 9,000 Prempro-related lawsuits filed in the United States to date. Of eight cases to go to trial, five have ended in “guilty” verdicts for the company. Pfizer has appealed all five.